There have been known battery packs having large power capacity, in which a plurality of prismatic cells, or battery modules, each consisting of a plurality of cells connected in series and coupled together in one piece, are arranged parallel with insulating spacers interposed therebetween. End plates are arranged at both ends in the direction of alignment of the cells or battery modules and tightly fastened with a restraining rod or a band, so as to prevent expansion of side faces of the cells or battery modules due to internal pressure of batteries. The cells or battery modules are connected either in series or in parallel (see, for example, Japanese Patent Laid-Open Publication No. 11-126585 and Published Japanese Translation No. 2001-507856 of PCT International Application).
In a battery pack of the above configuration, however, the end plates, as a restraining tool, need to have a rigidity that is high enough to withstand the internal pressure of the prismatic cells or the expansion of battery electrode plates, and in order to increase the rigidity, the end plates tend to be heavy and large, causing an increase in the weight and cost of the battery pack.
In view of the above problem in the conventional technique, it is an object of the present invention to provide a battery pack having a lighter restraining tool for achieving weight and cost reductions of the battery pack.